Various display devices such as a plasma display device, liquid crystal display device and an organic electro luminescence display device are used as a display device.
For example, a display device arranged with a movable type shutter formed using MEMS technology is proposed as a new display device as is shown in Japanese Laid Open Patent Application 2008-197668. An example of a movable type shutter 1 formed on a transparent substrate (SUB1) is shown in FIG. 6 and FIG. 7. FIG. 6 is a perspective view and FIG. 7 is a planar view.
A shutter (SH) is a structural component of the movable type shutter 1 having a flat plate shape and formed with an aperture part (OP1) which allows light to pass through. Furthermore, the shutter (that is, plate shaped shutter) is supported by four first springs (SP1, SP1′) arranged on both side of the shutter (SH). The base of the first spring (SP1, SP1′) is fixed to the substrate (SUB1) by an anchor part (AN1, AN1′). The first spring (SP1, SP1′) and shutter (SH) are held in a floating state from the substrate (SUB1). In addition, the base of second springs (SP2, SP2′) is fixed to the substrate (SUB1) by an anchor part (AN2, AN2′). The second spring (SP2, SP2′) is held in a floating state from the substrate (SUB1).
The surface of the first and second spring (SP1, SP1′, SP2, SP2′) is formed from a conductive material covered by an insulation film. In addition, each spring (SP1, SP1′, SP2, SP2′) conducts to a wire (not shown) arranged on the substrate (SUB1) via the anchor part (AN1, AN1′, AN2, AN2′).
A voltage is applied between anchor part AN1 and anchor part AN2 in order to drive the movable type shutter 1 in the arrow C direction shown in FIG. 7. Electric charges having respective polarities different from each other are accumulated in the first spring SP1 and the second spring SP2 thereby an electrostatic force is generated between the springs SP1, SP2, the springs SP1, SP2 are brought closer together and the first spring SP1 compresses in the arrow C direction. On the other hand, the same potential is applied to both of the first spring SP1′ and second spring SP2′. In this way, the first spring SP1′ extends in the arrow C direction.
Next, when the same potential exists both of the anchor part AN1 and anchor part AN2, the shutter SH moves in the arrow direction D in FIG. 7 by the rebound force of the first spring (SP1, SP1′) and second spring (SP2, SP2′), and returns to its original position. At this time, when a voltage is applied to both of the anchor part AN1′ and anchor part AN2′, the shutter SH moves even faster in the arrow D direction.
Another transparent substrate (not shown in the diagram) is arranged opposite the transparent substrate (SUB1) formed with the movable type shutter 1. An aperture which allows light to pass through is formed on the surface of this other substrate. In addition, when the shutter SH moves in the arrow C-D direction, the relative positional relationship between the position of the opening part (OP1) formed in the shutter and this aperture changes.
For example, in the case where a back light unit is arranged on the rear surface side of the substrate formed with an aperture, the opening part (OP1) and the position of the aperture overlap and light from the back light unit passes through, and when the position of the opening part (OP1) and the aperture are shifted from each other, the light from the back light is blocked by the shutter SH. In this way, it is possible to display an image by controlling (switching) the transmittance of the light from the back light unit.
In addition, in the case of displaying a color image, light sources corresponding to the three prime colors (RGB) are used as a back light unit. In addition, while each color light source is repeatedly flashed in sequence, an image of each color is displayed in sequence by driving the shutter on each pixel in synchronization with this flashing.
Because this type of MEMS display device does not use a polarization plate or color filter, the usage efficiency of light is high and significant power saving is possible even when compared to a plasma display device or liquid crystal display device. In addition, because a MEMS display device has a faster response speed than liquid crystal, it is possible to provide high video performance. In addition, a MEMS display device can realize high luminance and long life compared to an organic electro luminescence display device.
In a MEMS display device, it is necessary to arrange a transparent substrate (called a “first substrate” or “MEMS substrate”) arranged with a movable type shutter, and a transparent substrate (called a “second substrate” or “AP substrate”) formed with an aperture with a certain interval with a high level of precision. As a result, in a conventional MEMS display device, a plurality of supporting columns is formed on the AP substrate and a base which receives the columns is formed on the MEMS substrate.
FIG. 8 is a diagram which explains a part of the manufacturing process of a conventional MEMS display device. As is shown in FIG. 8, photo resist patterns RE1 and RE2 are formed in the shape corresponding to the structure of a movable type shutter or shape of the base on the first substrate (SUB1). The resist pattern RE1 is used in order to form a contact hole for obtaining conductivity from a wire arranged on the first substrate (SUB1) or in order to separate the shutter SH and first and second springs (SP1, SP1′, SP2, SP2′) from the first substrate (SUB1). The resist pattern RE2 is used in order to form the shape in a perpendicular direction (height direction in FIG. 3) of the shutter SH and first spring (SP1, SP1′) and second spring (SP2, SP2′).
In FIG. 8, a conductive film such as a semiconductor is formed on the surface of the resist patterns (RE1, RE2) in order to secure conductivity and a metal film (ME1) is stacked thereupon to secure light blocking effects. Next, a resist pattern RE3 corresponding to the planar surface shape of the shutter SH or first and second springs is formed.
Etching is performed using the resist pattern RE3, so that the shutter SH and first (SP1, SP1′) and second (SP2, SP2′) springs etc are formed. Following this, unnecessary parts of the resist patterns (RE1˜RE3) are removed and an insulation film IN is formed as in FIG. 8 (c) on the surface of the remaining metal film (ME1) and conducting film (CL).
The base PE arranged on the MEMS substrate is formed via the same manufacturing process as the shutter SH, first spring (SP1, SP1′), second spring (SP2, SP2′) and anchor part AN1.
On the other hand, a metal film (ME2) which becomes a light blocking film is formed on a transparent substrate (SUB2) for the AP substrate and the metal film of the aperture part is removed using a photo resist pattern in order to form an opening corresponding to the aperture. In addition, a column (CO) is formed on the metal film (ME2) by burning the photo resist as is shown in FIG. 8 (d).
The MEMS substrate (SUB1) and AP substrate (SUB2) are arranged opposite each other so as to bring the shutter SH and aperture closely facing each other. At this time, a tip end of the AP substrate support column (CO) is received by the base (PE) of the MEMS substrate.
The MEMS substrate and AP substrate are bound together by mechanically alignment using an alignment mark (not shown in the diagram) formed on each substrate. As a result, the alignment precision of the MEMS substrate and AP substrate is limited by the precision of a device for bonding the substrates together.
In addition, the base formed on the MEMS substrate and the supporting column formed on the AP substrate are both formed in a shape having a thickness in a height direction (vertical direction in the diagram) using a resist pattern. Therefore, when an external impact is received, the impact is not absorbed by the elasticity of the base itself formed on the MEMS substrate, which causes problems such as the supporting column on the AP substrate piercing the base, the surface of the base becoming chipped or misalignment between the support column and base. It is considered that the reason for this occurs is because a contact boundary between two parts the same material exists in case a projection (support column and base) is formed on each of two opposing substrates.
The aim of the present invention is to provide a display device in which self-alignment is performed during a bonding together process of a MEMS substrate and AP substrate and having a high level of reliability towards external impacts.